SIGMAR1 and cancer: In addition, Sig‐1R antagonists induce UPR activation and ER stress in adenocarcinoma cell lines, such as breast adenocarcinoma (MCF7) and prostate adenocarcinoma (PC3), which leads to the induction of autophagy and subsequent apoptotic activation, suggesting that UPR and autophagy induction mediate the cell protective effect of Sig‐1R in cancer cells.133